Alluvial or placer gold prospecting and mining conventional methods include panning, sluice box and more recently, suction dredging of placer deposits found in stream beds, creek beds and river beds. The latter method has become popular among recreational as well as professional placer gold mining and prospecting enthusiasts. The method involves suction to pull silt material from the benthic zones of streams, creeks and river bottoms into a suction hose via a pumping means, and onto a sluice box for separation of silt components by specific gravity or density. As an example, a typical suction dredging apparatus used for placer gold mining comprises a pump, which is often disposed on floating platform or raft. The bottom material comprises a fine silt composed primarily of silica sand and other finely divided minerals. Stones and pebbles of various sizes are also present. A suction hose is used to aspirate, or “vacuum” the bottom silt and small pebbles to a gold recovery system, such as a portable sluice box, may also be mounted on the same floating platform. In some configurations, the sluice box is assembled on the bank of the river, creek or stream, and is built as a permanent or semi-permanent structure on the shore.
In portable suction dredging operations, the sluice box has a short run, and may not be efficient. Siltification takes place as the silt effluent of the sluice box drops back into the water. This, in addition to the disruption of benthic and riparian habitat, current suction dredging practice creates serious environmental destruction for fish and other aquatic wildlife. Siltification causes increased turbidity, as well as release of toxic metals such as mercury into the water column. The state of California has already banned suction dredging in most streams and creeks to protect endangered aquatic species as well as cultural resources. While current suction dredging practices are damaging to the environment, improvements can be made by introduction of equipment of improved design and function to avoid many of the issues that threaten the continuation of the practice. In particular, significant reduction of siltification and bottom disruption is needed.
Panning is an ancient and popular form of batch prospecting of placer deposits for gold and precious stones and minerals. In contrast to suction dredging, it requires only a pan designed for the purpose. As an entirely manual prospecting technique, it is a slow and low yield process.